Multicolor tunable emission from organogels containing tetraphenylethene, perylenediimide, and spiropyran derivatives

Article abstract of DOI:10.1002/adfm.201000590

A dendron-substituted tetraphenylethene low molecular weight gelator (LMWG)compound, LMWG 1, is designed and investigated. Gelation-induced fl uorescence enhancement is observed for the gel based on LMWG 1 and its fl uorescence can be reversibly tuned by

Full text of DOI:10.1002/adfm.201000590

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Multicolor Tunable Emission from Organogels Containing
Tetraphenylethene, Perylenediimide, and Spiropyran
Derivatives
By Qun Chen, Deqing Zhang,* Guanxin Zhang, Xingyuan Yang, Yu Feng, Qinghua Fan,
and Daoben Zhu
utilizing the absorption spectral shifts
after gelation and effective fluorescence
resonance energy transfer process in
the organogel scaffold.[4] In a few cases,
gelation-induced-fluorescence-enhance-
ment was observed. Park and co-workers
reported the fluorescence increase after
gelation with 1-cyano-trans-1,2-bis-(3′5′-
bis-trifluoromethyl-biphenyl) ethylene(CN-
TFMBE).[5] Similar phenomena were
described for gelators with oxadiazole,[6a]
A dendron-substituted tetraphenylethene low molecular weight gelator
(LMWG)compound, LMWG1, is designed and investigated. Gelation-induced
fluorescence enhancement is observed for the gel based on LMWG1 and its flu-
orescence can be reversibly tuned by varying the temperature of the ensemble.
The photoinduced energy-transfer can occur between LMWG1 and PI2
(perylene diimide) in the gel phase, but it cannot occur in the corresponding
solution. The emission color of the gel of LMWG1 and PI2 can be tuned from
cyan, yellow, to red by varying the concentration of PI2. By taking advantage
of the photochromic transformation of spiropyran, the emission color of the
organogels based on LMWG1 and SP3 can be switched by alternating UV and
visible-light irradiations. The emission color can also be tuned by varying the
irradiation time. In this way, organogels based on LMWG1 with multiemission
color can be achieved in the presence of SP3 after light irradiations.
benzoxazole,[6b]
naphthalene[6c]
and
salicylideneaniline[6d] moieties. A significant
fluorescence enhancement was observed
for gelation with a gelator containing
anthracene and urea moieties as reported
by us recently.[7] Park and co-workers have
very recently described the emission tuning
for the organogels by light irradiations
apart from heating through incorporating the photochromic
compound into the gels.[8] Shinkai and co-workers found that
formation of assemblies of chromophores such as perylenedi-
imide after gelation could facilitate the energy-transfer proc-
esses and thus the organogels are potentially useful for light
harvesting.[9] In addition, it was found that the spectral features
of the “doping” compounds in the organogels can also be mod-
ulated after gelation. We and others successfully achieved the
thermal modulation of the pyrene monomer/excimer fluores-
cence by making use of the physical difference between gel and
solution phases.[10]
Silole and tetraphenylethene derivatives show abnormal fluo-
rescent behaviors; namely, they are weakly fluorescent in solution,
but they become strongly emissive after aggregation.[11] A few
silole and tetraphenylethene compounds were able to gel organic
solvents and gelation-induced fluorescence enhancement was
observed.[5,12] In this paper, we describe a new dendron-substituted
tetraphenylethene LMWG1 (Scheme 1). As anticipated, the fluo-
rescence intensity of LMWG1 increases significantly after gela-
tion and the fluorescence of LMWG1 can be reversibly modulated
by alternating heating and cooling. LMWG1 and PI2 (perylene
diimide, see Scheme 1) can form energy donor–acceptor pair as
there is a good spectral overlap between the fluorescence spectrum
of LMWG1 and the absorption spectrum of PI2. It is expected that
the photoinduced energy-transfer from LMWG1 to PI2 can be
tuned by taking advantage of AIE behavior of tetraphenylethene
compounds; in solution the energy transfer is not efficient
1. Introduction
Low-molecular weight gelators (LMWGs), which form three-
dimensional (3D) networks through weak intermolecular
interactions such as H-bonding, π–π stacking and van der
Waals forces, are capable of immobilizing solvent molecules
and forming organogels.[1,2] Because of the weak intermo-
lecular interactions, the gel-solution (sol) transitions for
these organogels are thermally reversible. It is interesting to
note that some physical properties can be tuned in accompa-
nying the corresponding gel-sol transitions for LMWGs.[3] For
instances, Ajayaghosh and co-workers reported a series of oligo
(p-pheylenevinylene)-derived LMWGs with tunable emission,
∗
[ ] Q. Chen, Prof. D. Q. Zhang, Dr. G. X. Zhang, X. Y. Yang, Y. Feng,
Prof. Q. H. Fan, Prof. D. B. Zhu
Beijing National Laboratory for Molecular Sciences
CAS Key Laboratories of Organic Solids
and Molecular Recognition and Function
Institute of Chemistry
Chinese Academy of Sciences
Beijing 100190 (China)
E-mail: dqzhang@iccas.ac.cn
Q. Chen, X. Y. Yang, Y. Feng
Graduate School of Chinese Academy of Sciences
Beijing, 100190 (China)
DOI: 10.1002/adfm.201000590
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O
O
O
O
DMF,K2CO3
ROH
DMF,K2CO3
Br(CH2)2Br
HBr/HOAc
Reflux
6
O
O
5
OH
O
4
LMWG1
Br
OR
MeOOC
COOMe
C12H25
12H25
C12H25
O
N
O
O
C12H25
O2N
MeOOC
MeOOC
O
C
N
O
C12H25
C12H25
O
O
N
SP
PI2
O
R
O
O2N
O2N
MeOOC
MeOOC
O
UV
Vis
N
O
O
O
SP3
MC
O
O
OR
N
COOMe
OR
MeOOC
Scheme 1. The molecular structures of LMWG1, PI2 and SP3; the synthetic route of LMWG1 and photochromic reaction of SP3.
with the dendron compound led to LMWG 1 in 80% yield. The
synthetic details and characterization were provided in Experi-
mental section.
because LMWG1 is non-fluorescent in solution, but in the gel
phase the energy transfer can occur efficiently. Moreover, it is
known that the absorption and fluorescence spectra of perylene
diimide are varied upon aggregation and thus they are dependent
on their concentrations.[13] Therefore, the emission color of the
ensemble of LMWG1 and PI2 can be tuned by varying the tem-
perature and the concentration of PI2 as shown in Scheme 2.
Alternatively, the merocyanine form (MC) of spiropyran that can
be easily generated by UV-light irradiation[14] shows absorption in
the range of 480–700 nm, and thus the MC form of spiropyran is
a good energy acceptor of LMWG1. Accordingly, the emission of
LMWG1 can be further tuned by light irradiation in the presence
of spiropyran (e.g., SP3 in Scheme 1), as schematically shown in
Scheme 2. In this way, the emission of LMWG1 can be success-
fully tuned by adjusting the temperature, concentration, and light
irradiation and multicolor emission can be achieved for organo-
gels containing LMWG1, PI2 and SP3 as to be discussed below.
The gelation ability of LMWG1 was examined. The results
show that LMWG1 can gel benzene (>20 mg mL−1) and toluene
(>20 mg mL−1). For example, a white translucent organogel
was formed by cooling the hot toluene solution of LMWG1
(20 mg mL−1) at 0 °C for 15.0 min. But, it cannot gel hexane,
cyclohexane, dichloromethane, acetonitrile, ethyl acetate, tet-
rahydrofuran, methanol and ethanol. As reported previously,
the multivalent π–π interactions due to the dendron group in
LMWG1 may be the driving-force for the gelation.[15] The xero-
gels of LMWG1 were characterized with scanning electron
microscopy (SEM), transmission electron microscopy (TEM)
and X-ray diffraction (XRD). Figure 1 shows the SEM and
TEM images of the xerogel formed with LMWG1 in toluene.
Molecules of LMWG1 are self-assembled into a 3D entangled
network of long thin nano-fibers with an average width of ca.
100 nm. The SEM and TEM images also show that big fibrous
nanostructures are composed of several twisted small nano-
fibers. Confocal laser scanning microscopy (CLSM) image
(Figure S1 in the Supporting Information) of the xerogel also
shows the same entangled fiber network. Only a broad peak at
0.305° (Figure S2), corresponding a d-spacing of 29 nm, was
detected in the XRD pattern. The relatively large d-spacing may
be related to the bulky dendron group in LMWG1.
2. Results and Discussion
2.1. Gel Formation, Characterization and Emission Modulation
for LMWG1
The synthesis of LMWG1 started from compound 4 which was
transformed into compound 5 after removal of one methyl
group. Compound 5 reacted with 1, 2-dibromoethane leading
to compound 6 in 80% yield. Further reaction of compound 6
The solution of LMWG1 (20 mg mL−1 in toluene) was almost
non-fluorescent as shown in Figure 2. But, the fluorescence of
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Scheme 2. Multicolor emission tuning for organogels formed with the ensemble of LMWG1, PI2 and SP3 by varying the temperature, concentration,
and light irradiation.
LMWG1 turned on after gelation; the fluorescence intensity at
490 nm was enhanced by 30 times after gelation. Such fluores-
cence enhancement is likely due to the fact that the intramo-
lecular rotations are restricted for the tetraphenylethene group
in LMWG1 in the gel phase, thus resulting in fluorescence
enhancement according to previous studies.[11] When the gel
was converted to solution after heating, the fluorescence of
LMWG1 became weak again. In this way, the fluorescence
intensity of LMWG1 can be reversibly modulated by alternating
cooling (transformation of the solution into organogel) and
heating (transformation of the gel into solution) as shown in
the inset of Figure 2.
18
15
12
9
16
12
8
Gel
Gel
Sol
4
Sol
0
1
2
3
4
5
6
Cycles
6
3
0
400
450
500
550
λ / nm
600
650
700
Figure 2. Fluorescence spectra of the solution and the corresponding
organogel formed with LMWG1 (20 mg mL−1) in toluene, λexc. = 365 nm;
inset shows the reversible fluorescence tuning by alternating heating and
cooling.
In addition, the fluorescence lifetimes of LMWG1 (20 mg mL−1
in toluene) in the gel phase were estimated to be τ1 = 1.09 ns
(47.2%) and τ2 = 4.33 ns (52.8%) by fitting the fluorescence
decay curve (see Figure S3). Similarly, the fluorescence life-
times of the corresponding solution of LMWG1 were estimated
to be τ1 = 0.18 ns (88.2%) and τ2 = 5.78 ns (11.8%) by fitting
the fluorescence decay curve (see Figure S4). Although τ2 of
LMWG1 in the gel phase was slightly shorter than that in the
solution, τ1 of LMWG1 in the gel phase was longer than that in
the solution. This is consistent with the significant fluorescence
enhancement of LMWG1 after gelation.[16]
Figure 1. SEM (a,b) and TEM (c,d) images of the xerogel prepared from
the organogel formed with LMWG1 (20 mg mL−1 in toluene).
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decay profile at 490 nm for the solution of LMWG1 (20 mg mL−1)
and PI2 (0.1 mM) (see Figure S11), the fluorescence lifetimes
of LMWG1 were estimated to be 0.29 ns (90.2%) and 6.11 ns
(9.8%). These lifetimes of LMWG1 in the presence of PI2 are
rather close to those of LMWG1 in the absence of PI2 (see
Figure S4). This result also implies that the photoinduced
energy-transfer from LMWG1 to PI2 in solution does not
occur.
18
Gel( LMWG1+PI2)
Sol( LMWG1+PI2)
Gel( LMWG1)
15
12
9
Sol( LMWG1)
The solution of LMWG1 and PI2 can be transformed into the
gel after cooling. As shown in Figure S8, where the SEM and
TEM images for the xerogel from LMWG1 (20 mg mL−1 in tol-
uene) and PI2 (10 mM) were shown, interconnected nanofibers
of widths ranging from ca. 100 nm to ca. 500 nm exist in the
xerogel. The big fibrous structures contain entangled thin-
nanofibers. The fluorescence spectrum (λex. = 365 nm) of the
gel was displayed in Figure 3. Both the fluorescence band in
the range 400–550 nm due to LMWG1 and that in the range
550–700 nm due to PI2 were observed after gelation; the fluo-
rescence intensity of organogel formed by LMWG1 at 485 nm
decreased by 31% after “doping” with PI2. By considering the
difference between the solution and gel phases of LMWG1
and PI2 in fluorescence spectrum, it can be concluded that the
photoinduced energy transfer between LMWG1 and PI2 is gov-
erned by the physical phase which is dependent on the tem-
perature of the ensemble.
The energy transfer efficiency between LMWG1 and PI2 can
be enhanced by increasing the concentration of PI2 in the gel
phase. The organogels based on LMWG1 with PI2 as “dopant”
can be easily prepared. By increasing the concentration of PI2
from 0.1 mM to 1.0 mM and 10 mM in the gel, the fluorescence
intensity (from 400 to 550 nm) due to LMWG1 decreased grad-
ually as shown in Figure 4. The corresponding energy transfer
efficiencies increased from 31% to 52% and 90%. Moreover,
the emission of the organogel containing LMWG1 and PI2 was
red-shifted by increasing the concentration of PI2 from 0.1 mM
to 1.0 mM and 10 mM in the gel, and the emission color was
changed from cyan to yellow and red, respectively (see Figure 4).
The variation of the emission color for the gel is attributed
to the fact that the emission spectrum of PI2 can be changed
6
3
0
400
450
500
550
λ / nm
600
650
700
Figure 3. Fluorescence spectra of organogels formed with LMWG1
(20 mg mL−1 in toluene) and PI2 (0.1 mM) and the corresponding solu-
tions; λexc. = 365 nm.
2.2. Emission Color Tuning for the Ensemble of LMWG 1 and PI2
PI2 was synthesized according to the reported procedure.[13b]
LMWG1 absorbs strongly at 365 nm while PI2 shows weak
absorption around 365 nm (Figures S5 and S6). Consequently,
it is possible to excite LMWG1 selectively in the presence of
PI2. As discussed above, PI2 is a good energy acceptor for
LMWG1 as the fluorescence spectrum of LMWG1 overlaps
well with the absorption spectrum of PI2 in the range of 400–
600 nm. However, the toluene solution composed of LMWG1
(20 mg mL−1) and PI2 (0.1 mM) was almost non-fluorescent
after excitation at 365 nm (see Figure 3). This is understand-
able by considering the fact that LMWG1 is weakly emissive
in solution; thus, the photoinduced energy-transfer from
LMWG1 to PI2 cannot take place efficiently in solution. In
fact, the fluorescence lifetimes of LMWG1 in the presence of
PI2 were also measured in solution. Based on the fluorescence
18
15
12
9
A B C D
A
B
C
D
6
3
0
400
450
500
550
/ nm
600
650
700
λ
Figure 4. Fluorescence spectra of organogels formed with LMWG1 (20 mg mL− 1) in toluene (A), and those of gels with LMWG1 (20 mg mL−1) in
toluene with different amounts of PI2 [0.1 mM (B), 1.0 mM (C) and 10 mM (D)], λexc. = 365 nm; photos of the organogels under daylight (top right) and
UV light (middle right), and the corresponding solutions under UV light (bottom right).
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upon aggregation by increasing its concentration. As shown
in Figure S6, the emission spectrum of PI2 was red-shifted by
100 nm when the concentration of PI2 increased from 0.1 mM
to 10 mM. These results clearly indicate that the emission color
of the gel based on LMWG1 and PI2 as “dopant” can be tuned
by varying the concentration of the “dopant”.
600
500
400
300
200
100
0
A
B
C
The photoinduced energy transfer process between LMWG1
and PI2 in the gel phase was investigated by measuring the
fluorescence life-times of LMWG1. The fluorescence decay
profiles of organogels at 490 nm were recorded with the exci-
tation wavelength of 365 nm. By fitting the fluorescence decay
profiles (see Figures S9–S13), the corresponding fluorescence
life-times were obtained for organogels of LMWG1 con-
taining different concentrations of PI2. As listed in Table 1,
compared to those of the gel in the absence of PI2 the fluo-
rescence life-times of gels of LMWG1 and PI2 are shortened
just slightly when the concentration of PI2 in the gels was not
higher than 1.0 mM. In these cases, the photoinduced energy
transfer between LMWG1 and PI2 proceeds probably with
emission-reabsorption mechanism (a trivial radiative mech-
anism). However, when the concentration of PI2 reached
10 mM, the corresponding life-times were obviously reduced.
When more PI2 was present in the gel phase, co-assembly
of LMWG1 and PI2 may occur; accordingly, molecules of
LMWG1 and PI2 may locate within a distance for effective
fluorescence resonance energy transfer through nonradiative
dipole-dipole coupling. Alternatively, the fluorescence life-
times of PI2 in the organogels based on LMWG1 and PI2 were
measured by recording the corresponding fluorescence decay
profiles of organogels at either 580 nm or 650 nm[17] with the
excitation wavelength of 365 nm. The decay curves shown in
Figures S14–16 were fitted with a biexponential function and
the lifetimes were listed in Table S1. It is obvious that the
fluorescence intensity at either 580 nm or 650 nm (mainly
due to PI2) decays more slowly and excited states with long
lifetimes emerged gradually by increasing the concentration
of PI2 in the gels. This may be ascribed to the formation of
self-assembly aggregates of PI2 at high concentration and as
a result long-lived excited states can be generated according
to previous report.[13b]
450 500 550
600 650
/ nm
700 750
λ
Figure 5. Fluorescence spectra of the organogels formed with LMWG
1 (20 mg mL−1) and SP (4.0 mg mL−1) in toluene (A), after UV light
(365 nm) irradiation for 10 min (B) and further visible light (550 nm)
irradiation for 10 min (C); λexc. = 400 nm.
form which exhibits absorption in the range of 480–700 nm.[14]
Therefore, the MC form can function as the energy acceptor
for LMWG1 as mentioned above. The organogels of LMWG1
containing simple SP compound (1,3,3-trimethylindolino-6′-
nitrobenzopyrylospiran, Scheme 1) can be prepared similarly
by cooling the corresponding hot solutions. As an example,
Figure 5 shows the fluorescence spectrum of the organogel
formed with a hot toluene solution composed of LMWG1
(20 mg mL−1) and SP (4.0 mg mL−1). Compared to the corre-
sponding solution, the organogel exhibited strong emission
around 490 nm.[18] But, the emission intensity of the organogel
was reduced by 75% after UV light (365 nm) irradiation for
10 min. This is likely due to the formation of MC form of SP
after UV light irradiation and consequently the photoinduced
energy transfer between MC form and LMWG1 can occur,
leading to the decrease of the emission intensity of LMWG1.
The emission intensity of the organogel can be recovered after
further visible light (550 nm) irradiation as shown in Figure 5.
In this manner, the emission intensity of the organogel of
LMWG1 can be switched off and on by alternating UV and vis-
ible light irradiations.
2.3. Emission Color Tuning for the Ensemble of LMWG1 and SP3
SP3, a dendron-substituted spiropyran (see Scheme 1), was
synthesized and purified with the reported procedure.[15b] We
have very recently described the gelation based on SP3 and it is
interesting to note that (i) the gel-phase was kept after the trans-
formation of the open form of SP into the MC form induced by
UV light irradiation, (ii) the gel absorbed strongly in the range of
480–700 nm after UV light irradiation, and (iii) the gel based on
the MC form of SP3 exhibited strong red emission.[15b] There-
fore, it is appealing to examine the emission color tuning for the
organogels based on LMWG1 and SP3. Similarly, the organogel
formed by LMWG1 (10mM) and SP3 (10 mM) was prepared
by cooling the corresponding toluene solution. The xerogel
was also characterized with SEM and TEM (see Figure S17).
The SEM image shows that the xerogel contains densely-packed
entangled nanofibers with the average width of ca. 200 nm.
Small nanofibers of different widths are bound together to form
It is known that the photochromic SP compound can be revers-
ibly transformed into the corresponding MC (merocyanine)
T a b le 1 . Fluorescence lifetimes of organogels formed with LMWG1
(20 mg mL−1) in toluene (A), and those of gels with LMWG1 (20 mg mL−1
)
in toluene with different doping concentrations of PI2 [0.1 mM (B),
1.0 mM (C) and 10mM (D)]; the fluorescence intensity at 490 nm was
monitored; λexc. = 365 nm.
Organogels
τ1(ns)
τ2 (ns)
A
B
C
D
1.091 0.020(47.24%)
1.082 0.019(47.91%)
0.939 0.018(45.28%)
0.541 0.013(52.09%)
4.334 0.034(52.76%)
4.270 0.032(52.09%)
4.274 0.030(54.72%)
3.431 0.025(47.91%)
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changed from initial blue to pink and red
after UV light (365 nm) irradiation for 30 s
and 10.0 min, respectively (see Figure 6).
It was also found that the fluorescence
intensity at 650 nm decreased and that at
490 nm increased gradually when the gel of
LMWG1/SP3 that was exposed to UV light
for 10 min was left in dark for different
times as depicted in Figure S20. This is
understandable by considering the fact that
the MC form of SP3 can be transformed
into the closed form in the dark gradually;
as a result the photoinduced energy transfer
between LMWG1 and the MC form of SP3
cannot occur efficiently. The fluorescence
decay at 650 nm was also measured for the
gel based on LMWG1/SP3 that was exposed
to UV light for 10 min (see Figure S21).
But, the fluorescence intensity at 650 nm
decays very quickly.
150
160
490 nm
650 nm
A
B
C
D
120
90
140
60
120
30
0
1
2
3
4
5
6
Cy cles
100
80
60
40
20
0
450 500 550 600 650 700 750 800
Similar emission spectral change was
also observed for the organogels based on
LMWG1/SP3 in different molar ratios (see
Figures S22–S24); the more amount of SP3
in the gel, the weaker is the emission inten-
sity in the range of 425–575 nm and the
stronger is the emission intensity in the
range of 575–650 nm after UV light irradia-
tion. This is because more MC form of SP3
λ / nm
Figure 6. Fluorescence spectra of the organogel formed with LMWG1 (10 mM) and SP3
(10 mM) in toluene (A), after UV light (365 nm) irradiation for 30 s (B) and 10 min (C), and
further visible light (550 nm) irradiation for 10 min (D), λexc. = 400 nm; the inset shows the
reversible variation of fluorescence intensities at 490 nm and 650 nm upon alternating UV and
visible light irradiations, and photos of the organogels irradiated under UV light immediately
(blue), after 30 s (pink) and 10 min (red), respectively.
is generated after UV light irradiation if more SP3 is present in
gel and consequently the corresponding photoinduced energy
transfer will take place more efficiently.
large fibers based on the TEM image. As expected, the emission
was switched on after gelation, but the emission intensity of gel
with LMWG1 and SP3 decreased compared to that of the gel
with pure LMWG1 (see Figure S18).[19]
Figure 6 shows the emission spectrum of the gel based on
LMWG1/SP3 and those after UV light (365 nm) irradiation for
30 s, 10 min, and further visible light irradiation for 10.0 min.
The emission in the range of 425–575 nm due to LMWG1
became weak after UV light irradiation and simultaneously
the emission in the range of 575–750 nm, due to the MC form
of SP3 according to previous report,[15b] emerged. Such emis-
sion spectral change is owing to the photoinduced energy
transfer between LMWG1 and the corresponding MC form
of SP3. The photoinduced energy transfer between LMWG1
and the MC form of SP3 should be responsible for emission
spectral change for the gel based on LMWG1/SP3 after UV
light irradiation. The fluorescence life-times (Figure S19)
of the gel at 490 nm based on LMWG1/SP3 after UV light
irradiation for 10.0 min were estimated to be 0.25 ns (78.9%)
and 1.64 ns (21.1%). Compared to those of the gel with pure
LMWG1 listed in Table 1, the fluorescence life-times of the
gel based on LMWG1/SP3 were obviously shortened. This
is in agreement with the emission spectral change. More-
over, the emission spectrum could be resumed after further
visible light irradiation. Accordingly, the emission inten-
sities at 490 nm and 650 nm of the gel based on LMWG1/
SP3 can be reversibly tuned by UV–visible light irradiations
as depicted in the inset of Figure 6. Additionally, the emis-
sion color of the gel of LMWG1/SP3 was also dependent
on the UV light irradiation time and the emission color
3. Conclusion
By making use of the AIE behavior of tetraphenylethene
derivatives, a dendron-substituted tetraphenylethene com-
pound as a new organogelator (LMWG1) was designed and
investigated. Gelation-induced fluorescence enhancement
was observed for the gel based on LMWG1 and its fluores-
cence can be reversibly tuned by varying the temperature of
the ensemble. The photoinduced energy-transfer can occur
between LMWG1 and PI2 in the gel phase, but it cannot
occur in the corresponding solution. Furthermore, the emis-
sion life-times of the gel of LMWG1 and PI2 as a “dopant”
indicate that the photoinduced energy transfer occur more
efficiently by increasing the concentration of PI2. As a
result, the emission color of the gel of LMWG1 and PI2 can
be tuned by varying the concentration of PI2. By taking the
advantage of the photochromic transformation of spiropyran,
the emission color of the organogels based on LMWG1 and
SP3 can be switched by alternating UV and visible light irra-
diations. The emission color can be also tuned by varying the
irradiation time. In this way, organogels based on LMWG1
with multiemission color can be achieved in the presence
of SP3 after light irradiations. Such organogels with tunable
emission colors may find applications in various areas such
as data recording.
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119.0, 118.9, 114.0,113.9, 113.7, 113.3, 113.2, 70.2, 70.0, 66.8, 66.4, 55.2,
52.6; MALDI-TOF-MS (m/z): 1598.4 [M]+, 1621.4 [M + Na]+; Anal. calcd.
for C93H82O25: C, 69.83; H, 5.17. Found: C, 69.79; H, 5.21.
Gel Formation: In a typical gelation experiment, a weighed amount of
LMWG1 and 1.0 mL of the solvent were placed in a test tube, which was
sealed and then heated until the sample was dissolved. Then, the hot
solution was slowly cooled in ice water. The gels containing either PI2 or
SP3 were prepared similarly.
4. Experimental Section
General: Unless otherwise stated, all starting materials and reagents
were purchased from commercial suppliers and used without further
purification. The solvents used were dried and purified by standard
methods prior to use. 1H NMR and 13C NMR spectra were recorded
with Bruker 400 MHz spectrometers. Mass spectra were determined
with BEFLEX III for TOF-MS and SHIMADZU GCMS-QP2010 for EI-MS.
Elemental analysis was performed on a Carlo-Erba-1106 instrument.
A confocal laser scanning microscopy system (CLSM, FV-1000-IX81
Olympus, Japan) was employed. XRD data were collected on a Rigaku
D/max-2500 X-ray diffractometer with Cu Kα radiation. For SEM
CLSM images, XRD data, SEM images, TEM images, absorption and
fluorescence spectra, fluorescence lifetime, and 1H-NMR and 13C-NMR
spectra are available in the Supporting Information.
experiments,
a JEOL JSM 6700F field-emission scanning electron
microscope was used, and the frozen dried xerogel was sputtered
with platinum. TEM measurements were conducted with a JEOL 2010 Supporting Information
transmission electron microscopes using an accelerating rate voltage
Supporting Information is available from the Wiley Online Library or
from the author.
of 120 keV. Absorption spectra were recorded on a JASCO V-570
spectrophotometer. Fluorescent spectra were measured with a Hitachi
F-4500 spectrophotometer. Fluorescence lifetimes were measured by
using an Edinburgh Analytical Instruments (FLS920) and evaluated
with the software designed for the equipment. The fluorescence decay
were fitted by deconvoluting the instrument response with biexponential
decay: Fit = A + B1exp(−t/τ1) + B2exp(−t/τ2). The quality of fit was judged
by the value of χ2 and visual inspection of the residuals.
Synthesis of Compound 5: Compound 4 was synthesized according to
the literature.[11f ] To a 100 mL flask was added 4 (2.36 g, 6.0 mmol) and
acetic acid (40 mL). Then, HBr (12 mL, 33% in HOAc w/w) was added
and the mixture was refluxed at 120 °C for 12 hours. After cooling to room
temperature, it was poured into water (500 mL). The precipitate was
filtered and purified by column chromatography on silica with petroleum
ether (60–90 °C)/ethyl acetate (6/1, v/v) as eluent. Compound 5
(680 mg) was obtained as light yellow solid powder in 30% yield. 1H
NMR (400 MHz, CDCl3, 25 °C, TMS): δ = 7.08 (m, 10H), 6.92 (m, 4H),
6.64 (m, 2H), 6.56 (m, 2H), 4.71 (s, 1H), 3.75 (s, 3H); 13C NMR (100 MHz,
CDCl3, 25 °C): δ = 158.1, 154.0, 144.4, 144.3, 139.9, 139.7, 136.8, 136.6,
136.5, 132.9, 132.7, 131.5, 127.8, 127.7, 126.4, 114.8, 114.7, 113.4, 113.2,
55.3; EI-MS (m/z): 378 [M]+; Anal. calcd. for C27H22O2: C, 85.69; H, 5.86.
Found: C, 85.70; H, 6.10.
Synthesis of Compound 6: To a flask (50 mL) were added compound 5
(567 mg, 1.5 mmol), dimethylformamide (DMF, 20 mL), 1,
2-dibromoethane (1.3 mL, 15 mmol) and K2CO3 (1.38 g, 10 mmol).
The mixture was stirred at room temperature for 3 days. Then it was
poured into water (80 mL) and extracted with dichloromethane. The
organic layer was washed with water (80 mL) for five times and dried
over Na2SO4. The solution was purified by column chromatography on
silica gel with petroleum ether (60–90 °C)/ethyl acetate (10/1, v/v) as
eluent. Compound 6 (582 mg) was obtained as light yellow solid powder
in 80% yield. 1H NMR (400 MHz, CDCl3, 25 °C, TMS): δ = 7.10 (m,
10H), 6.99 (m, 4H), 6.67 (m, 4H), 4.24 (m, 2H), 3.75 (s, 3H), 3.61 (m,
2H); 13C NMR (100 MHz, CDCl3, 25 °C): δ = 158.2, 156.6, 144.4, 144.3,
140.1, 139.6, 137.4, 136.5, 132.8, 132.7, 131.6, 127.9,127.8, 126.4, 114.1,
114.0,113.3, 113.2, 67.9, 55.3, 29.3; EI-MS (m/z): 484 and 486 [M]+; Anal.
calcd. for C29H25BrO2: C, 71.76; H, 5.19; Br, 16.46. Found: C, 71.72; H,
5.20; Br, 16.35.
Synthesis of LMWG1: To a flask (50 mL) were added compound 6
(484 mg, 1.0 mmol), DMF (20 mL), ROH (R = dendron group, Scheme 1)
(1.19 g, 1.0 mmol) and K2CO3 (1.38 g, 1.0 mmol). The mixture was stirred
at room temperature for 3 days. Then it was poured into water (80 mL)
and extracted with dichloromethane. The organic layer was washed with
water (80 mL) for five times and dried over Na2SO4. The solution was
purified by column chromatography on silica gel with dichloromethane/
ethyl acetate (30/1, v/v) as eluent. LMWG1 (1.28 g) was obtained as
light yellow solid powder in 80% yield. 1H NMR (400 MHz, CDCl3, 25 °C,
TMS): δ = 8.29 (s, 4H), 7.82 (s, 8H), 7.12–6.89 (m, 23H), 6.68–6.63
(m, 4H), 5.12–5.09 (s, 12H), 4.31–4.25 (m, 4H), 3.93 (s, 24H), 3.73
(s, 3H); 13C NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 166.2, 159.5,
159.4, 158.8, 158.1, 157.1, 144.4, 144.3, 140.0, 139.7, 138.9, 138.4, 137.0,
136.5, 132.8, 132.7, 132.0, 131.5, 127.8, 127.7, 126.4, 126.2, 123.5, 120.3,
Acknowledgements
The present research was financially supported by NSFC, the State Basic
Program and Chinese Academy of Sciences. This work was partially
supported by the NSFC-DFG joint project (TRR61). The kind help from
Prof. A. Xia is appreciated with regard to the fluorescence lifetimes
measurements. The authors thank the anonymous reviewers for the
comments and suggestions, which enable us to improve the manuscript.
Received: March 27, 2010
Revised: May 21, 2010
Published online: August 4, 2010
[1] a) P. Terech, R. G. Weiss, Chem. Rev. 1997, 97, 3133;
b) N. M. Sangeetha, U. Maitra, Chem. Soc. Rev. 2005, 34, 821;
c) P. Dastidar, Chem. Soc. Rev. 2008, 37, 2699; d) L. A. Estroff,
A. D. Hamilton, Chem. Rev. 2004, 104, 1201; e) D. J. Abdallah,
R. G. Weiss, Adv. Mater. 2000, 12, 1237; f) J. H. van Esch, B. L. Feringa,
Angew. Chem. Inter. Ed. 2000, 39, 2263; g) S. Banerjee, R. K. Das,
U. Maitra, J. Mater. Chem. 2009, 19, 6649; i) M. George, R. G. Weiss,
Acc. Chem. Res. 2006, 39, 489; j) R. G. Weiss, Langmuir 2009, 25,
8369, and articles from that special issue.
[2] a) S. Kawano, N. Fujita, S. Shinkai, Chem. Eur. J. 2005, 11, 4735;
b) S. Kawano, N. Fujita, S. Shinkai, J. Am. Chem. Soc. 2004, 126,
8592; c) T. Kitahara, M. Shirakawa, S. Kawano, U. Beginn, N. Fujita,
S. Shinkai, J. Am. Chem. Soc. 2005, 127, 14980; d) S. Wang,
W. Shen, Y. L. Feng, H. Tian, Chem. Commun. 2006, 1497;
e) L. L. Zhu, X. Ma, F. Y. Ji, Q. C. Wang, H. Tian, Chem. Eur. J.
2007, 13, 9216; f) R. Wang, C. Geiger, L. H. Chen, B. Swanson,
D. G. Whitten, J. Am. Chem. Soc. 2000, 122, 2399; g) P. Gao,
C. L. Zhan, M. H. Liu, Langmuir 2006, 22, 775; h) Y. G. Li, T. Y. Wang,
M. H. Liu, Soft Matter 2007, 3, 1312; i) Y. L. Zhao, I. Aprahamian,
A. Trabolsi, N. Erina, J. F. Stoddart, J. Am. Chem. Soc. 2008, 130,
6348; j) C. Wang, D. Q. Zhang, D. B. Zhu, J. Am. Chem. Soc. 2005,
127, 16372; k) C. Wang, Q. Chen, F. Sun, D. Q. Zhang, G. X. Zhang,
Y. Y. Huang, R. Zhao, D. B. Zhu, J. Am. Chem. Soc. 2010, 132, 3092.
[3] a) J. J. D. de Jong, T. D. Tiemersma-Wegman, J. H. van Esch,
B. L. Feringa, J. Am. Chem. Soc. 2005, 127, 13804; b) J. J. D. de Jong,
L. N. Lucas, R. M. Kellogg, J. H. van Esch, B. L. Feringa, Science
2004, 304, 278; c) C. Wang, D. Q. Zhang, D. B. Zhu, Langmuir 2007,
23, 1478.
[4] a) A. Ajayaghosh, V. K. Praveen, C. Vijayakumar, Chem. Soc. Rev.
2008, 37, 109; b) A. Ajayaghosh, V. K. Praveen, Acc. Chem. Res.
2007, 40, 644; c) A. Ajayaghosh, S. J. George, A. P. H. J. Schenning,
Top. Curr. Chem. 2005, 258, 83; d) A. Ajayaghosh, S. J. George,
©
3250 wileyonlinelibrary.com
2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2010, 20, 3244–3251

www.afm-journal.de
www.MaterialsViews.com
J. Am. Chem. Soc. 2001, 123, 5148; e) A. Ajayaghosh, R. Varghese,
V. K. Praveen, S. Mahesh, Angew. Chem. Int. Ed. 2006, 45, 3261; f)
V. K. Praveen, S. J. George, R. Varghese, C. Vijayakumar, A. Ajayaghosh,
J. Am. Chem. Soc. 2006, 128, 7542. g) A. Ajayaghosh, C. Vijayakumar,
V. K. Praveen, S. S. Babu, R. Varghese, J. Am. Chem. Soc. 2006, 128,
7174; f) D. Dasgupta, S. Srinivasan, C. Rochas, A. Ajayaghosh,
J. M. Guenet, Langmuir 2009, 25, 8593; g) A. Ajayaghosh,
V. K. Praveen, C. Vijayakumar, S. J. George, Angew. Chem. Int. Ed.
2007, 46, 6260; h) A. Ajayaghosh, V. K. Praveen, S. Srinivasan,
R. Varghese, Adv. Mater. 2007, 19, 411; i) C. Vijayakumar, V. K. Praveen,
A. Ajayaghosh, Adv. Mater. 2009, 21, 2059; j) S. S. Babu, Vakayil
K. Praveen, S. Prasanthkumar, A. Ajayaghosh, Chem. Eur. J. 2008,
14, 9577.
[12] M. Wang, D. Q. Zhang, G. X. Zhang, D. B. Zhu, Chem. Phys. Lett.
2009, 475, 64.
[13] a) F. Würthner, Chem. Commun. 2004, 1564; b) F. Würthner,
Z. J. Chen, V. Dehm, V. Stepanenko, Chem. Commun. 2006, 1188;
c) X. Q. Li, V. Stepanenko, Z. J. Chen, P. Prins, L. D. A. Siebbeles,
F. Würthner, Chem. Commun. 2006, 3871; d) C. C. You, P. Espindola,
C. Hippius, J. Heinze, F. Würthner, Adv. Funct. Mater. 2007, 17,
3764; e) C. Thalacker, F. Würthner, Adv. Funct. Mater. 2002, 12, 209.
[14] a) G. Y. Jiang, Y. L. Song, X. F. Guo, D. Q. Zhang, D. B. Zhu, Adv.
Mater. 2008, 20, 2888; b) F. M. Raymo, Adv. Mater. 2002, 14, 401;
c) F. M. Raymo, M. Tomasulo, Chem. Soc. Rev. 2005, 34, 327;
d) X. F. Guo, D. Q. Zhang, Y. Gui, M. X. Wan, J. C. Li, Y. Q. Liu,
D. B. Zhu, Adv. Mater. 2004, 16, 636–640; e) G. Y. Wen, J. Yan,
Y. C. Zhou, D. Q. Zhang, L. Q. Mao, D. B. Zhu, Chem. Comm.
2006, 3016; f) X. F. Guo, D. Q. Zhang, D. B. Zhu, J. Phys. Chem. B
2004, 108, 212; g) J. L. Bahr, G. Kodis, L. de la Garza, S. Lin,
A. L. Moore, T. A. Moore, D. Gust J. Am. Chem. Soc. 2001, 123,
7124; h) J. Andréasson, S. D. Straight, G. Kodis, C. D. Park,
M. Hambourger, M. Gervaldo, B. Albinsson, T. A. Moore,
A. L. Moore, D. Gust, J. Am. Chem. Soc. 2006, 128, 16259.
[15] a) Y. Feng, Z. T. Liu, J. Liu, Y. M. Liu, Q. Y. Zheng, Q. H. Fang,
J. Am. Chem. Soc. 2009, 131, 7950; b) Q. Chen, Y. Feng, D. Q. Zhang,
G. X. Zhang, Q. H. Fan, S. N. Sun, D. B. Zhu, Adv. Funct. Mater.
2010, 20, 36.
[5] B. K. An, D. S. Lee, J. S. Lee, Y. S. Park, H. S. Song, S. Y. Park,
J. Am. Chem. Soc. 2004, 126, 10232.
[6] a) S. V. Ryu, S. Kim, J. W. Seo, Y-W. Kim, O. H. Kwon, D. J. Jang,
S. Y. Park, Chem. Commun. 2004, 70; b) T. H. Kim, M. S. Choi,
B-H. Sohn, S. Y. Park, W. S. Lyoo, T. S. Lee, Chem. Commun. 2008,
2364; c) H. Yang, T. Yi, Z. G. Zhou, Y. F. Zhou, J. C. Wu, M. Xu,
F. Y. Li, C. H. Huang, Langmuir 2007, 23, 8224; d) P. C. Xue, R. Lu,
G. J. Chen, Y. Zhang, H. Nomoto, M. Takafuji, H. Ihara, Chem. Eur. J.
2007, 13, 8231.
[7] C. Wang, D. Q. Zhang, J. F. Xiang, D. B. Zhu, Langmuir 2007, 23,
9195.
[8] J. W. Chuang, S. J. Yoon, S. J. Lim, B. K. An, S. Y. Park, Angew. Chem.
Int. Ed. 2009, 48, 7030.
[9] K. Sugiyasu, N. Fujita, S. Shinkai, Angew. Chem. Int. Ed. 2004, 43,
1229.
[16] It should be noted that the fluorescence decay curves of LMWG1
cannot be fitted with a single-exponential function, but they can be
well fitted with a bi-exponential function. Therefore, two lifetimes
were deduced for LMWG1 in the gel phase and solution. Such two
lifetimes may be ascribed to different conformations of LMWG1 in
the excited states by considering bulky dendron group in LMWG1
and the intermolecular interactions in the gel phase.
[17] When the concentration of PI2 in the gel was not higher than 10
mM, the emission intensity at 650 nm was very weak. For this
reason the fluorescence decay was measured by monitoring the
fluorescence intensity at 580 nm, at which LMWG1 also exhibits
emission. But, the fluorescence intensity at 580 nm should be
mainly due to PI2.
[18] A weak emission around 660 nm was detected. This may be due to
the fact that small amount of MC form of SP was formed during the
measurement.
[19] This may be understood by considering the fact the SP3 is a typical
electron donor and as a result photoinduced electron transfer may
occur between SP3 and LMWG1.
[10] a) C. Wang, Z. Wang, D. Q. Zhang, D. B. Zhu, Chem. Phys. Lett.
2006, 428, 130; b) Y. Kamikawa, T. Kato, Langmuir 2007, 23, 274.
[11] a) Y. N. Hong, J. W. Y. Lam, B. Z. Tang, Chem. Commun. 2009, 4332;
b) M. Wang, G. X. Zhang, D. Q. Zhang, D. B. Zhu, B. Z. Tang, J. Mater.
Chem. 2010, 20, 1858; c) L. H. Peng, G. X. Zhang, D. Q. Zhang,
J. F. Xiang, R. Zhao, Y. L. Wang, D. B. Zhu, Org. Lett. 2009, 11, 4014;
d) L. Liu, G. X. Zhang, J. F. Xiang, D. Q. Zhang, D. B. Zhu, Org. Lett.
2008, 10, 4581; e) M. Wang, X. G. Gu, G. X. Zhang, D. Q. Zhang,
D. B. Zhu, Anal. Chem. 2009, 81, 4444; f) H. Tong, Y. N. Hong,
Y. Q. Dong, M. Haussler, Z. Li, J. W. Y. Lam, Y. P. Dong, H. H. Y. Sung,
I. D. Williams, B. Z. Tang, J. Phys. Chem. B 2007, 111, 11817;
g) L. Tang, J. K. Jin, A. J. Qin, W. Z. Yuan, Y. Mao, J. Mei, J. Z. Sun,
B. Z. Tang, Chem. Commun. 2009, 4974. h) H. Tong, Y. N. Hong,
Y. Q. Dong, M. Haubler, J. W. Y. Lam, Z. Li, Z. F. Guo, Z. H. Guo,
B. Z. Tang, Chem. Commun. 2006, 3705.
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Adv. Funct. Mater. 2010, 20, 3244–3251
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